Two primary “ink-jet” or “pulse-jet” type printers exist. One type, commonly described as a “bubble jet” printer, works by vaporizing propellant in a liquid print medium inside a nozzle with a small resistive heater to create a bubble that displaces the liquid therein through an orifice toward a target. The other type uses piezoelectric elements to displace and drive liquid print medium through a nozzle orifice.
Especially when used to deposit substances other than ink, such printheads are sometimes referred to as “pulse-jet” devices in the alternative. Regardless of their designation, the printheads operate by delivering a pulse of pressure (e.g., by a piezoelectric or thermoelectric element as noted above) to liquid adjacent an outlet or orifice such that a drop will be dispensed therefrom.
Ink-jet/pulse-jet syle printheads have come to be used in a variety of applications. A popular use of such devices is printing ink on paper. Another use is in producing “biochips” or arrays in which fluid compositions of binding agents e.g., bipolymers such as oligonucleotides and peptides, or precursors thereof, e.g., amino acid or nucleotide residues, are deposited onto a solid support surface in the form of an array or pattern.
Pulse-jet devices may be used to produce such arrays or microarrays with other apparatus and methods as described in U.S. patent application Ser. No. 09/150,504 titled, “Method and Apparatus for Making Nucleic Acid Arrays”; U.S. patent application Ser. No. 09/300,589 titled, “Method of Performing Array-Based Hybridization Assays Using Thermal Inkjet Deposition of Sample Fluids”; U.S. patent application Ser. No. 09/846,474 titled “Error Detection In Chemical Array Fabrication”; and U.S. Pat. Nos. 6,242,266 and 6,180,351. Other components or array printing systems which may be adapted for use with the present invention include those used to dispense bio/chemical agents such as proteins and nucleic acids as described in U.S. Pat. Nos. 4,877,745; 5,338,688; 5,474,796; 5,449,754; 5,700,637; and 5,658,802.
Whether used for producing arrays, dispensing fluid samples, in connection with known methodology as in the references noted or otherwise, the present invention addresses a number of well-known problems with ink-jet or pulse-jet printheads. These problems include proper pressure maintainance at the printhead level during print medium reservoir depletion and avoiding air entrapment that disrupts printhead function.
The present invention addresses problems associated with pressure maintenance through optional pressure equilization/maintenance features. In each type of printhead noted above, the nozzles typically have an open orifice. Ideally, cappilary forces hold liquid in the nozzles ready for dispensing. However, too much negative pressure on a fluid supply at the nozzle overcomes the capillary action. This excessive negative pressure causes printhead malfunction through nozzle arration. Further, the stop junction provided at the nozzle end can be breached when overly high fluid supply pressures are applied. Such a breach causes the nozzle to drip.
Providing proper fluid supply pressure can be particularly difficult in connection with large fluid supply reservoirs, where liquid levels can vary greatly with respect to printhead level as print medium is consumed. Sometimes, partial vacuum or air pressure is applied to a reservoir in an effort to balance pressure effects. The present invention offers a highly effective approach, particularly where large fluid reservoirs are concerned.
Also, certain features of the present invention address air entrapment issues presented by ink-jet or pulse-jet systems. Before a printhead is used, it must be fully filled in order to operate reliably. A small bubble trapped at a critical location (such as in the vicinity of a piezoelectric element or bubble generator) can prevent firing. Optional features of the invention avoid the need for air purging upon changing a fluid reservoir. These features also allow for supply change-out during printhead operation.
Those with skill in the art may well appreciate further utility or possible advantages in connection with the invention described herein. Whatever the case, it is contemplated that some variations of the invention will only afford certain advantages, while others will present all of them.